This invention relates generally to systems and methods for treating cooling tower water and, more specifically, to a system and method for treating cooling tower water utilizing a high concentration ozone generation apparatus.
Cooling towers are utilized in a variety of processes, such as refrigeration and steam power generation, to remove heat generated by the process. Generally, the cooling tower is part of a system in which water is circulated to a heat exchanger, which is located at a part of a system (for example condenser coils in a large refrigeration system) having heat that needs to be removed. The cooling tower water absorbs the heat at the heat exchanger, and the heated water is then piped to the cooling tower, where it is sprayed into the atmosphere and partially evaporated to liberate the heat, and then recovered and returned at a lower temperature to the system, where the process repeats itself.
Because of minerals, biological contaminants and other matter contained in cooling tower water, cooling tower systems are vulnerable to deposits (scaling), biofouling, and other types of damage. For example, calcium bicarbonate present in water of the type typically used in cooling towers will stay in solution to about 2,000 parts per million (ppm). However, when the water is heated, the calcium bicarbonate becomes calcium carbonate, with carbon dioxide being given off. Calcium carbonate is far less soluble than calcium bicarbonate, and will only stay in solution to about 10 parts per million. (This phenomenon is known as inverse solubilityxe2x80x94since it is the reverse of the common principle that solubility generally increases as the temperature of the solution is raised.) Calcium carbonate coming out of solution forms deposits in the system, including in particular at the heat exchanger. The formation of deposits on the heat exchanger will reduce the efficiency of the system.
Biological fouling is also a significant problem. Microbiological contaminants can enter a cooling tower system through the water introduced into the system or by being washed from the air during the cooling process. As these contaminants grow, they can interfere with water flow and/or foul the heat exchanger, restricting heat flow. Such contaminants can also destroy cooling tower lumber. More seriously, such contaminants can be harmful to persons. The most notable example has been outbreaks of Legionnaires"" disease, affecting people in hotels, hospitals, office buildings, and other locations, who have come into contact with cooled air from an air conditioning system cooled with contaminated cooling tower water.
A number of methods have been developed to treat cooling tower water, so as to address these and related problems. These generally fall into two categories: chemical addition and bleed-off control. With respect to the former, for example, the problem of hardness has been treated by removing the calcium hardness or scale forming mineral from the water prior to its introduction to the systemxe2x80x94with lime soda, ion exchange, or reverse osmosis. Another chemical addition method is to keep scale forming minerals in solution by increasing their solubility through the addition of acid to the water. Still another is to add crystal modifying chemicals that will allow the minerals to precipitate out as a non-adhering sludge instead of as a hard deposit. Biofouling has been addressed with the introduction of chemical biocides into the water, including oxidizing chemicals and industrial poisons. Drawbacks to chemical addition treatment methods include that some of the chemicals used are toxic; a chemical treatment that is effective in dealing with one problem (e.g., increasing alkalinity to control corrosion) can aggravate another problem (e.g., increased alkalinity promotes scaling); and cost.
Bleed-off control, the other basic treatment method, addresses problems associated with impurities in cooling tower water by removing a portion of the water contained in the cooling system so as to reduce the concentration of impurities. However, the increasing cost of water has made it desirable to operate a cooling tower with as little bleed as possible.
In recent years, ozone has attracted attention as a treatment method for cooling tower water. Ozone is an unstable molecule comprised of three atoms of oxygen (O3) having a high oxidation potential. Its ability to purify water and air is well known. It was used to purify drinking water by the latter part of the 1800""s, and today is used for this purpose by most major U.S. cities. Ozone has also been utilized for the purification of other types of water, including waste water and irrigation water. Still further, ozone has been used for purifying the air in food storage facilities going back at least as far as 1909.
The basic principles underlying the use of ozone generation are well established. Clean, dry air consists of approximately 78 percent nitrogen gas (N2), approximately 21 percent oxygen gas (O2), and less than one percent of hydrogen (H2) and other gasses. When air (referred to as the xe2x80x9cfeed gasxe2x80x9d in this context) is irradiated using either an ultraviolet source or corona discharge (the acceleration of electrons between two electrodes, separated by a dielectric material, to collide with a feed gas passed therebetween), some of the O2 molecules are split to form two short-lived oxygen atoms. These oxygen atoms combine, almost instantaneously, with uncleaved oxygen molecules to form ozone.
Ozone is not the only product of what is generally referred to herein as an ozonation process; i.e., the irradiation of a feed gas to create ozone and other new compounds. The bombarding of the feed gas with electrons causes the all of the component gassesxe2x80x94and not just the oxygen to rearrangexe2x80x94forming a number of beneficial molecular combinations in addition to ozone. These rearranged molecules include nitrates, nitrites, nitrogen oxides, nitric acid, nitrogen based acids, hydrogen peroxide, hydroperoxide, and hydroxyl radicals (NO, NO2, NO3, N2O, N2O5, HNO2, HNO3, O, H, OH, HO2, H2O2).
Ozone and certain of the other atoms and molecules formed as a result of ozonation have a number of beneficial uses in the areas of disinfection and water softeningxe2x80x94and are therefore particularly useful in the treatment of cooling tower water.
Ultraviolet radiation is disfavored as a method for generating ozone, due to the inability to produce high quantities of ozone at a relatively low cost in this fashion. As a result, most commercial ozone production is accomplished using a corona discharge type of ozone generator.
However, there are numerous problems with prior art corona discharge ozone generators, and thus limitations on their suitability for use in a system and method for treating cooling tower water. Thus, when the feed gas is passed between the electrodes, water or dust present in the feed gas attach themselves to the dielectric surrounding the cathode. These spots tend to attract electrons, with the result that hot spots are formed on the surface of the dielectricxe2x80x94leading eventually to the burning through of the dielectric and consequent failure of the generation apparatus. In the commercial area, ozone generators require constant servicing and, indeed, rebuilding, because of such problems. In the City of Los Angeles, for example, high concentration ozone generators used to treat the city""s drinking water are presently required to be rebuilt after approximately ten days of usexe2x80x94a rate that is plainly undesirable. Moreover, prior art devices do not permit the ready manipulation of the ozonation products, for example to produce more ozone and less nitrogen-containing compounds or more nitrogen-containing products and less ozone.
Still further, prior art systems for treating cooling tower water based on ozonation do not utilize a centrifuge to further assist in the process of removing separated materials, resulting in a less efficient process.
U.S. Pat. No. 4,954,321, issued to the applicant herein, illustrates a plasma corona discharge apparatus, representing an improvement upon the basic corona discharge process. Generally, a plasma corona discharge apparatus is similar to a non-plasma apparatus, except that in a plasma apparatus, an inert gas is inserted into an elongated, insulated, sealed cathode, into which electrons are fired for the ozonation process. That gas performs two functions. First, it generally precludes the formation of hot spots and resulting dielectric burn-through and generator failure through a convection process. In this regard, the inert gas, which has become a plasma by virtue of the electrons passing therethrough, becomes attracted to a water or dust spot, the gas becomes heated and then rises away from the hot spot, to be replaced by gas having a lower temperature. This results in a relatively constant movement of the gas and substantially reduces overheating and/or apparatus failure attributable to the formation of stable hot spots.
The second function of the inert gas is to directly assist in the efficiency of the ozonation process. In this regard, upon the firing of electrons from an electron gun into the inert gas, a plasma is formed within the cathode (i.e., on the inside of the dielectric), and also outside of the dielectric. The passage of electrons though this plasma and into the feed gas causes oxygen disassociation and reformation as ozone at an improved rate over non-plasma devices.
However, even the plasma device illustrated in U.S. Pat. No. 4,954,321, while more reliable than prior art devices, suffers from important limitations and deficiencies. For example, the energy produced by the electron gun firing into the cathode is concentrated near the electron gun, and gradually dissipates over the length of the electrode. This results in a decrease in the effectiveness of this particular prior art apparatus in treating the feed gas, and thus in the production of a lower concentration of ozone than is possible if the energy level could be maintained constant throughout the length of the cathode.
A need therefore existed for an improved system and method for treating cooling tower water, based on an ozone generator apparatus and method capable of reliably generating high concentrations of ozone (and other ozonation products) suitable for use in such treatment. The improved system and method should provide for the maintenance of a relatively constant energy level throughout the length of the energy-producing electrode, so as to provide more efficient production of ozonation products. The improved system and method should also provide for the efficient adjustment of the products of ozonation, so that ozone or nitrogen-containing products can be favored. The improved system and method should further utilize a centrifuge, to further assist in the process of removing separated materials. The present invention satisfies these needs and provides other, related, advantages.
It is an object of the present invention to provide an improved system and method for treating cooling tower water with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons.
It is an object of this invention to provide an improved system and method for treating cooling tower water with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons, wherein the system and method have a reduced risk of failure as compared to prior art systems and method based on corona discharge apparatuses.
It is a further object of this invention to provide an improved system and method for treating cooling tower water with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons capable of producing a higher concentration of ozone than prior art systems and methods based on corona discharge apparatuses by, among other things, providing for a substantially constant energy level throughout the length of the first electrode in the apparatus used in the system and method of the present invention.
It is a still further object of this invention to provide an improved system and method for treating cooling tower water with ozone and other atoms and molecules formed from the bombardment of a feed gas with electrons which system and method may be readily adjusted to alter the relative quantities of atoms and molecules produced from the bombardment, so as to optionally produce more oxidizing compounds or more nitrogen containing compounds.
In accordance with one embodiment of the present invention, a system for treating cooling tower water is disclosed. The system comprises, in combination: an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules comprising: a first electrode; wherein the first electrode comprises: an electron gun coupled to a power source and located proximate one end of the first electrode; a rod in electrical communication with the electron gun; a first tube of dielectric material disposed along a length of the rod; a second tube of dielectric material dimensioned to receive therein the first tube; wherein the second tube is substantially sealed; and an inert gas disposed within each of the first tube and the second tube; a second electrode containing a channel dimensioned to receive therein the first electrode so that sufficient space is present between the first electrode and the second electrode that a feed gas may be passed through the channel along an exterior surface of the first electrode; a feed gas inlet coupled to the second electrode and wherein the feed gas inlet is in communication with the channel; and a feed gas outlet coupled at a first end thereof to the second electrode and wherein the feed gas outlet is in communication with the channel; and an injector coupled to the feed gas outlet.
In accordance with another embodiment of the present invention, a system for treating cooling tower water is disclosed. The system comprises, in combination: an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules comprising: a first electrode comprising a substantially sealed tube of dielectric material; wherein the first electrode further comprises: a first electron gun coupled to a power source, located proximate one end of the first electrode, and adapted to fire electrons into the substantially sealed tube of dielectric material; a second electron gun coupled to a power source, located proximate a second end of the first electrode, and adapted to fire electrons into the substantially sealed tube of dielectric material; and an inert gas disposed within the substantially sealed tube of dielectric material; a second electrode containing a channel dimensioned to receive therein the first electrode so that sufficient space is present between the first electrode and the second electrode that a feed gas may be passed through the channel along an exterior surface of the first electrode; a feed gas inlet coupled to the second electrode and wherein the feed gas inlet is in communication with the channel; a feed gas outlet coupled at a first end thereof to the second electrode and wherein the feed gas outlet is in communication with the channel; and an injector coupled to the feed gas outlet.
In accordance with still another embodiment of the present invention, a system for treating cooling tower water is disclosed. The system comprises, in combination: an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules; an injector coupled to the apparatus and adapted to inject the feed gas into cooling tower water; a centrifuge coupled to the injector and adapted to centrifuge the cooling tower water following the injection of the feed gas into the water; and wherein the centrifuge is coupled to a cooling tower system.
In accordance with yet another embodiment of the present invention, a method for treating cooling tower water is disclosed. The method comprises the steps of: providing an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules comprising: a first electrode; wherein the first electrode comprises: an electron gun coupled to a power source and located proximate one end of the first electrode; a rod in electrical communication with the electron gun; a first tube of dielectric material disposed along a length of the rod; a second tube of dielectric material dimensioned to receive therein the first tube; wherein the second tube is substantially sealed; and an inert gas disposed within each of the first tube and the second tube; a second electrode containing a channel dimensioned to receive therein the first electrode so that sufficient space is present between the first electrode and the second electrode that a feed gas may be passed through the channel along an exterior surface of the first electrode; a feed gas inlet coupled to the second electrode and wherein the feed gas inlet is in communication with the channel; and a feed gas outlet coupled at a first end thereof to the second electrode and wherein the feed gas outlet is in communication with the channel; providing an injector coupled to the feed gas outlet; providing power from the power source to the electron gun; passing a feed gas into the feed gas inlet, through the channel, and out of the feed gas outlet; and injecting the feed gas passing out of the feed gas outlet into cooling tower water.
In accordance with another embodiment of the present invention, a method for treating cooling tower water is disclosed. The method comprises the steps of: providing an apparatus for bombarding a feed gas with electrons to generate ozone and other atoms and molecules; providing an injector coupled to the apparatus and adapted to inject the feed gas into cooling tower water; providing a centrifuge coupled to the injector and adapted to centrifuge the cooling tower water following the injection of the feed gas into the cooling tower water; bombarding the feed gas with electrons; injecting the bombarded feed gas with the injector into the cooling tower water; centrifuging the cooling tower water in the centrifuge; removing from the cooling tower water in the centrifuge separated materials; and passing the cooling tower water into a cooling tower system.